Amazon.com offers the Feline Pine Original Cat Litter 20-lb. Bag for $9.89. Choose Subscribe & Save and it falls to $8.41 and yields free shipping. That's the lowest total price we could find for a bag of this size by $16. It's made from 100% neutral southern yellow pine shavings and guar bean gum.

Of note, Subscribe & Save can be easily canceled after your order arrives, but be sure to do so or you'll be billed for subsequent shipments.